Managing director Ron Allum spoke to PM as he sat above Challenger Deep, the deepest known point of the world's oceans.

Mr Allum says the divers will spend the majority of their time in vertical ascent and descent.

"When you look at the profile of the dive we spend the majority of the time in vertical ascent and descent and very little time in horizontal flight," he said.

"If he can quicken up the descent and then the ascent [it will maximise our time] on the bottom.

"We do have good forward movement in any case. We have six horizontal thrusters that are proving to be quite powerful."

Mr Allum will be on board the submarine with Cameron and a team of scientists, including experts in plate tectonics and biologists.

"We've got science well and truly covered," he said.

"My role in the expedition is purely to build the expedition vehicle, overcome all the hurdles associated with that, and I leave the science to other people.

"I just hope I've made a vehicle that is a utility for scientists."

Under pressure

Mr Allum says he is confident the submarine will be able to withstand the intense pressure at the ocean's floor.

"We've done a lot of engineering on the way and a lot of our products have been tested," he said.

"If you look at every little piece of the submersible, we're sure every piece has been pressure tested in a chamber.

"We glued the whole assembly together. We don't have a pressure chamber big enough to test it; we're literally going to put it in the ocean."

Mr Allum says he was chosen to build the sub in Sydney because of his prior work with Cameron.

"I've been on quite a few expeditions with Jim Cameron where we field Ghosts of the Abyss, Aliens of the Deep, we did a Discovery special on the Bismarck and also we did a live telecast from the Titanic in 2005," he said.

"I've had a bit of experience working with James Cameron. I guess one thing led to another, we get talking on boats, especially when they're en route to location, and this came up some years ago.

"My job was a broadcast tech basically - my job was to make things happen - and basically what I've done is made a camera, some amazing cameras, to go down to the bottom of the ocean."

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